Earthquake Performance of Nonstructural Components
January 2003
Poor performance of nonstructural components,
equipment, and systems is the greatest contributor to damage, losses, and business
interruption for most facilities after an earthquake. The cost of loss of operations,
service, market share, and business continuity or interruption can exceed the
value of the building itself. The new International Building Code incorporates
more stringent design requirements for nonstructural components, and buildings
in compliance should show greater earthquake risk tolerance.
by Nathan
C. Gould, D.Sc., P.E., S.E. and Michael J. Griffin, P.E.
ABS Consulting
The importance of good earthquake performance of nonstructural components,
equipment, and systems required for post-earthquake recovery and facility function/operation
is often overshadowed by the focus on building structural damage. A review of
the typical damage sustained in recent earthquakes highlights the fact that
the poor performance of nonstructural components, equipment, and systems is
the greatest contributor to damage, losses, and business interruption for most
facilities.
Structural versus Nonstructural Elements
Structural elements are typically components associated with the primary
building structure used to provide the support and environmental enclosure for
the facility functions. Nonstructural items support the function of the facility
and typically include the following.
- Architectural Components
- cladding
- interior partition walls
- ceilings and lights
- raised computer floor systems
- racks and shelving
- Equipment and Systems
- Electrical power
and distribution systems
- Heating, ventilation, and cooling systems
- Fire protection systems
- Emergency power generation
- Building Contents and Inventory
-
Record storage
- Production equipment and systems
- Supplies/inventory
- Computer equipment
For many facilities, particularly manufacturing or production facilities,
the value of nonstructural components, equipment, and systems will typically
exceed the value of the building structure itself. In a moderate earthquake,
damage to critical equipment and contents may be more important than damage
to buildings. In addition, damage to such equipment can lead to extended business
interruption due to lost production and even a loss in market share. In many
cases, business interruption may pose a corporation’s greatest earthquake financial
risk.
Historical Performance of Nonstructural Components
Past earthquakes can teach us valuable lessons regarding the vulnerabilities
of nonstructural systems to even moderate levels of ground motion. For example,
the 1994 Northridge Earthquake caused significant nonstructural damage to a
number of area hospitals. In these instances, the hospitals remained structurally
sound, but required closure due to significant damage to nonstructural components—primarily
water damage and loss of emergency utility function. The problem lies in the
treatment of these commodities in the building design codes.
The primary types of failures experienced by nonstructural components can
be classified as either inertial failures or displacement/deformation failures.
Inertial failures are failures caused by:
- Excessive shaking of the component
- Component rocking due to unanchored or marginally anchored conditions
- Component sliding due to unanchored conditions
Good examples of inertial failures are shown below with the sliding rooftop
AC units on the left and the overturned computer equipment shown on the right.
Displacement / Deformation failures are failures caused by:
- Excessive building inter-story displacements or drift
- Incompatible stiffness between the building structure and component
- Interaction between adjacent structural systems and nonstructural systems
- Multiple structure connection points
Good examples of displacement/deformation type failures are shown below with
the displaced ceiling grid on the left and a deformed architectural glazed wall
on the right.
Losses Due to Nonstructural Damage
The impact from earthquake damage to a building or facility owner can frequently
go well beyond the typical damage that is often depicted in post-earthquake
photographs. The damage can be classified as either direct property damage or
indirect property damage. Indirect property damage may include:
- Loss of operations
- Loss of service
- Loss of market share
- Business continuity or interruption
The photographs below illustrate the type of events that can lead to additional
indirect losses above and beyond that of the direct damage loss that initiated
the event. The photograph on the left depicts the flooding that occurred in
a facility after a sprinkler pipe failure. Note, there was no fire following
the earthquake for this facility.
The photograph on the right shows a common type of electrical panel failure
that can often lead to further business interruption. Extended business interruption
can result if specialty equipment is damaged due to the potential long lead
times for equipment procurement, construction, shipping, and installation.
The losses due to business interruption, which are greatly influenced by
nonstructural damage, can often equal or exceed losses due to the actual damage
to the structure and equipment. The chart below compares the projected earthquake
losses for a Midwest manufacturing facility. As shown by the chart, the loss
due to business interruption, cleanup, and recovery is roughly equal to the
total expected direct damage loss for the facility. Furthermore, the total expected
loss exceeds the total value—buildings, equipment, and inventory, of the facility.
Graph
1
Building Codes and Nonstructural Components
Traditional model building codes, such as the Standard Building Code, BOCA,
and UBC have not concentrated on the seismic design of nonstructural components,
equipment, and systems. In fact, the model codes are defined as a minimum design
requirement for the purpose of protecting life-safety. The model codes are not
designed for the purpose of providing property damage protection to a building
and its contents. In fact, acceptable building performance under the model codes
can be a damage state that allows for the safe egress of building occupants
from the building with no life-safe injuries, but the building sustains significant
damage such that it is uneconomical to repair and return to service.
Probably the most important link in having the ability to quickly repair
and resume facility function is the proper performance of equipment and systems.
And, this is where the model codes contain less in their proper specification
of design provisions.
The current interpretation and application of the model codes for equipment
and systems is to treat them as independent components.
Most vendor equipment and system design agencies believe that if the equipment
has been installed with seismically designed anchorage, it will perform adequately
during and following a seismic event. This is true for approximately 75-80 percent
of equipment installations. However, it is the internal component support and
the interdependencies of the equipment systems that have often shown the greatest
vulnerability for damage when subjected to earthquake ground motion. The identification
of these key vulnerabilities and the specification of the proper seismic design
criteria is imperative in order to ensure that the performance objective of
continued function following a major earthquake is satisfied.
Since the 1964 Alaska and 1971 San Fernando earthquakes, the codes have attempted
to increase both the scope and strictness of nonstructural seismic design provisions
in an attempt to achieve better performance. It is within the last several code
editions that the seismic design provisions for these commodities have begun
to address the real issues in assuring the proper performance of nonstructural
components, equipment, and systems when subjected to major earthquake events.
The new International Building Code (IBC) issued to replace the three model
building codes in use throughout the United States incorporates more stringent
design requirements for nonstructural components, which should aid in reducing
the damage to nonstructural components. Specifically, the IBC:
- Uses increased design forces relative to most of the model building
codes
- Incorporates significantly greater prescriptive requirements for nonstructural
components than most model building codes
- Specifies additional drift design provisions
- Incorporates additional and more specific requirements for anchorage
design
- Requires the component itself to be seismically designed when the equipment
is designated to have a higher level of importance (Ip>1.0); i.e., for hospitals,
fire stations, police stations, etc.
Summary
The importance of properly designing, constructing, and installing nonstructural
components in order to reduce the losses due to earthquakes cannot be overstated.
As history has demonstrated, damage to nonstructural components in past earthquakes
has resulted in the majority of the direct property losses. Additionally, the
damage to nonstructural components can contribute to increased indirect losses
due to business interruption and loss of market share. It therefore becomes
incumbent on the building owner to understand the intended purpose of the model
building design codes related to the expected, and acceptable, earthquake performance
of the facility in establishing earthquake risk tolerance.
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